The invention relates to a cathode ray tube having an envelope comprising a phosphor screen on one side and a neck portion on the other side, and an electron gun which is positioned in the neck portion and has a beam-shaping part and a focusing structure, said beam-shaping part comprising a cathode and at least one metal electrode, and said focusing structure comprising a hollow tube which is open at both ends and is made of an electrically insulating material with a layer of high-ohmic resistive material on the inner surface.
Such a cathode ray tube is known from EP-A No. 233379. The cathode ray tube described in this Application is provided with an electron gun which comprises a hollow glass tube. In the manufacture the glass tube is softened by heating it and is drawn on an accurately made mandril which changes diameter several times in its longitudinal direction. Supporting faces for the electrodes of the beam-shaping part of the gun are formed on the inside of the tube thus calibrated. The focusing structure is constituted by a layer of high-ohmic resistive material which is provided, for example, in a helical form on the inner wall of the glass tube.
If such a "glass" gun is manufactured in large numbers, it is found that the very accurately made (and hence expensive) mandrils required during manufacture wear rapidly. This is at the expense of the reproducibility. Moreover, it appears to be a problem to make the electrode components to be accommodated in the glass tube in a sufficiently constant shape.